The present invention relates to an analog display instrument, in particular for use in dashboards in motor vehicles.
Disc indicators of this generic type have bearings for instruments on motor vehicles. In this case, the only instruments which are referred to as “disc indicators” in this context are those in which the indicator disc is not held on a shaft that is mounted such that it can rotate, but the indicator disc is mounted such that a guided ring structure allows the indicator disc to rotate. Finally, the special feature of disc indicators such as these is that there is no need for the central shaft. This results in a high degree of flexibility with regard to the design options for the instrument.
One disc indicator of this type is disclosed, for example, in DE 199 16 221 A1, which has a disc to which the pointer is fitted, with the disc being held between two guide rollers at its outer edge. In this case, one of the rollers is driven by a stepping motor.
In DE 199 03 202 A1, covers are fitted with pointer symbols, have a circular external contour and are mounted in the cutouts in a board or panel such that they can rotate. In this case, rolling elements are fitted in the covers in order to minimize the friction in the bearing. The drive which initiates the rotary movement is provided by an electric motor, which acts on a toothed rim on the cover.
EP 492 543 A1 describes a pointer plate which is driven by an annular ultrasound motor in such a way that the pointer plate is connected to the rotor of this ultrasound motor such that they rotate together, by the edge of the pointer plate being formed such that it is oriented orthogonally with respect to the plate plane, thus producing a holder for the rotor part of the ultrasound motor. No radial bearing is formed by this design.
In consequence, the types of bearing specified for disc indicators are complex with a large number of components, resulting in correspondingly expensive manufacturing costs. Furthermore, instruments such as these may be less reliable in operation. Although disc indicators have a number of advantages over conventional instruments which have a pointer held at the end of a shaft, it has not until now been possible to make use of these instruments, particularly because of the high production costs.